“Part of the job of deputy leader is to support the leader by making sure they’ve got their feet anchored very firmly in the real world.”

She opens up about the “shame” of Wendy Flint’s fatal addiction - and the “chaos” it created in the household.

Ms Flint has spoken before of her mother’s lost battle with the bottle, but always stepped back from detailing the daily difficulties dealt to family life.

Today, in a highly-personal interview, she explains how struggling to cope with Wendy’s illness helped toughen her for the world of politics.

Wendy, who had split from her husband - Ms Flint’s step-dad - suffered from low self-esteem.

Caroline said her mum found comfort in alcohol, swigging “what she could afford”.

Her daughter, the 53-year-old feisty frontbencher known for her combative style on TV, is quiet and reflective as she recalls the home life of her teens.

“You go to school and you try to get on with things, but you’re never quite sure what you’re going to come home to,” says Ms Flint.

“There’s a lot you do as a child to keep things private.”

She feared what pals would say if they discovered the family’s secret.

“You’re ashamed about it, you’re worried about people finding out, you’re worried what people will think of your mum, you’re worried what people will think of you, you’re worried about what’s happening to your brother and sister - and obviously you’re worried about your mum and what she might do when the drink takes hold,” admits Ms Flint.

“For any children going through this, it’s a mixed emotion because you can go through love and hate in 24 hours, and you just don’t know from one day to the next what emotions you’re going to be feeling.”

When Ms Flint “escaped” to the University of East Anglia in the 1980s, she volunteered for a student counselling helpline - and urged her younger brother and sister to call with updates on their mum.

“This is before mobile phones so I would tell my sister when I was going to be doing my duty so she could ring me up and keep me in touch with what was happening,” she admits.

Not every day dealing with Wendy's alcoholism was “a sad day”, says Ms Flint.

“It’s important to understand it’s not all doom and gloom all the time,” says the former Public Health Minister, switching between the past and present tenses.

“My mum was a lovely, beautiful woman with a great sense of humour and one of the kindest people you could meet.

“She worked most of her life, even with the alcohol problem. But when the alcohol takes hold, it’s really difficult - and that’s not the same mum.”

Twenty-five years since Wendy’s death, Ms Flint only drinks socially and never by herself.

“I never drink alone,” she says. “If I drink alcohol, I drink with my friends and husband socially - not that I think I’m going to go off the rails or anything, but I don’t want to be that person who takes refuge in alcohol on your own, because that’s when it does take a grip.

“For me, that is my line. That, for me, is just a no-no.”

She believes her difficult upbringing and a string of low-paid jobs in her late teens and 20s have “definitely had an influence” on her personality, and given her experience she feels are lacking in her rivals for the number two role - bookies’ favourite Tom Watson, ex-Culture Secretary Ben Bradshaw, Shadow Commons Leader Angela Eagle and campaigning MP Stella Creasy.

She says she would work with the shock frontrunner in the race for the leadership, Jeremy Corbyn, if he wins.

“I will serve as deputy leader with any of the leadership candidates,” stresses Ms Flint, refusing to say who she backs.

“Part of the job of deputy leader is to support the leader by making sure they’ve got their feet anchored very firmly in the real world.”

Policies needed to withstand scrutiny as well as command public respect, the Shadow Minister says, adding: “One of the best badges you can have as a party is one of competence - that’s when you start getting people’s trust back.”

And calling on the victor to “broaden” Labour’s appeal, blunt Ms Flint warns: “If we don’t, we’re not going to win an election in 2020.”